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Wilbour
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# Posted: 28 Oct 2014 08:02
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I have had advise from both sides and still I am not sure what to do. I have a loft that's the full footprint of my 10 x 16 cabin. The peak is 5' and the pitch is 12/12. The roof is 2 x 4 16" OC.
I can either use the foam venting channels to encourage ventilation and fiberglass around that but once I put T & G over that there will not be much room left for the insulation.
The other alternative is to use rigid foam on the inside of the rafters and T & G over that. The issue is there is not much room to move a big sheet up to the loft now but I am leaning this way. It gives me lots of ventilation and should go up quick. If I do this, what sort of fasteners could I use? Regular nails but stop short of denting the rigid foam?
I don't want to use rigid foam in between the rafters since they are odd spacing and they will bounce around with the wind (we have lots of wind)
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bldginsp
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# Posted: 28 Oct 2014 08:52 - Edited by: bldginsp
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With only 2x4 rafters you have very little depth for insulation. With the 1" air space above that leaves you 2-1/2". That much fiberglass is not going to give you much benefit, hardly worth the effort. If you squeeze R13 in there with the 1" vent channels, you will compress the insulation which reduces it's effectiveness. If you opt for this I'd suggest using R11, cause it is thinner and won't compress. With fiberglass you need loft.
Despite the added expense and difficulty of using rigid foam, I suggest you use that. To hold it in place firmly you can use spray foam cans around the edges in whatever gaps to 'glue' it in place.
Very wise of you to ventilate above the insulation, in any circumstance.
One other alternative is closed cel spray foam for the entire ceiling, but that's real expensive and you have to hire someone to come out and do it. I think there are some DIY spray foam kits but not sure.
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Wilbour
Member
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# Posted: 28 Oct 2014 09:26
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We are not too concerned about the R value since the cabin is really just a 3 season place. It's more about the drafts and condensation. I like the idea of "Spray foam around the edges". That may just work. I could also cut small spacers to keep the foam away from the outer sheathing.
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MtnDon
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# Posted: 28 Oct 2014 10:21
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To install rigid foam sheets over wall studs or rafters use these nylon washers.
I have also seen them on Amazon and ebay. They spread the force over the larger area w/o danger of pull through. Be careful though as it is still possible to crush into the foam more than you want. They are meant to be tightened just enough to make a small dimple so whatever is placed over lays flat.
The exterior walls of our home are all covered in XPS foam held in place with these.
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creeky
Member
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# Posted: 28 Oct 2014 16:06
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You can buy the above washers with nails attached at any big box hardware store. Depending on your insulation thickness.
I used polyiso due to it's higher r value per inch. plus it comes with a neat reflective foil! (humour implied) plus the foil will reflect heat both ways ... i don't know if you have a vented soffit/peak but that's a great idea ...
Put the panels over your joists not between. Nail. tape or infill with spray foam. install t&g. have fun.
you want to get fancy and add summer time stack effect cooling see my shizzer shack build ... google creeky shizzer shack.
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